With an ever increasing number of people purchasing recreational vehicles, it is of the upmost importance that stability between the tow vehicle and the trailer be maintained while traveling at turnpike speeds. One form of instability exhibited by these vehicles is swaying, where the trailer oscillates back and forth similar to a pendulum. Another stability problem can occur during a quick lane change. This can result in severe yawing in the trailer which can lead to loss of control of the tow vehicle. Similar yawing can be caused by passing or being passed by a semi-trailer or by a gusty crosswind. In addition, two vehicle-trailer combinations have a critical speed above which control is difficult or impossible to uniformly maintain. This critical speed is usually somewhat slower than the desired speed for highway driving creating a hindrance for a smooth traffic flow pattern.
To alleviate these sway stability problems some of the larger trailers are equipped with damping or spring devices attached to the hitch. These damping devices normally consist of at least one shock absorber located on opposite sides of the tongue of the trailer. These devices improve trailer control at low speeds, but do not effect the critical speed so that the safe speed is still limited.
In addition, stiffening of the sidewalls of the tires on the trailer have helped to dampen some of the sway forces when traveling at low speeds. However, it has been found that at high speeds the damping characteristics of the tires have little overall effect on the total oscillatory movement of the trailer.
In U.S. Pat. No. 3,893,692, incorporated herein by reference, an anti-sway apparatus is disclosed which has a comparator that can supply an actuation signal for applying a servomotor in the trailer when an oscillary force reaches a predetermined value. A first sensor is located in the front and a second sensor is located in the rear of the trailer while the comparator is located at the center of gravity of the vehicle. As long as the first and second sensors supply substantially the same indication of movement in the trailer, the comparator will remain inactive. However, due to the cost and critical limitations necessary to properly install the first and second sensors, this approach has not received substantial industry approval.